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TCA9555

Introduction

TCA9555 is a Python module for interfacing the Texas Instruments TCA9555 16-bit I2C-based GPIO expander using a Raspberry Pi. All public methods are thread-safe which allows for continuous reading / writing to the GPIO from mutliple threads.

Installation

You have to have Python >= 2.7 with the following packages installed:

To install these dependecies, open a terminal and type

pip install wiringpi bitstring

Then, to finally install TCA9555, move to the root folder and type

python setup.py develop

which will install in development mode

Setup

To use this module, you need to enable the I2C interface of your Raspberry Pi

sudo raspi-config

Navigate to the advanced options - I2C menu and select enable. Now you need to connect the Raspberry Pis I2C pinout to the respective TCA9555 pins

 Role | Rpi | TCA9555
------|-----|--------
 SDA  |  3  |   23   
 SCL  |  5  |   22   
 GND  |  6  |   12   
 VCC  |  5  |   24

If you do not plan to set a custom address to your TCA9555, tie address pins A0, A1 & A2 to GND as well. This will result in an IC2-bus address of 0x20 (32).

Examples

Basic usage

Below you'll find a selection of use-cases. To see all available methods, please check here

# Import the class
from tca9555 import TCA9555

# Initialize with standard I2C-bus address of TCA9555 a.k.a 0x20
gpio = TCA9555()

# Print startup-config as human-readable
print(gpio.format_config())

# Set pins 0, 1, 2 as output
gpio.set_output(bits=(0,1,2))

# Write value 5 to bits 0, 1, 2
gpio.int_to_bits(bits=(0,1,2), val=5)

# Read value from bits 0, 1, 2 
print(gpio.int_from_bits(bits=(0,1,2)))  # 5

# Check if bit 0 is high
gpio.is_high(0)

# Set bit 1 and 2
gpio.set_bits(bits=(1, 2))

# Unset bits 2
gpio.unset_bits(bits=2)

Multi-threaded usage

A more advanced scenario is that certain pins of the GPIO expander are used to read a value, while others are used to set registers / logic levels of other ICs. Such a scenario is shown below

# Imports
from tca9555 import TCA9555
from threading import Thread, Event

def continuous_read(pins):
    """Read continuously from *pins* until *flag* is set"""
    while not flag.is_set():
        res = gpio.int_from_bits(bits=pins)
        print(res)

# Initialize GPIO expander
gpio = TCA9555()

# Initialize flag to stop thread
flag = Event()

# Read 4 bit integer from pins 0 to 3
read_pins = (0, 1, 2, 3)

# Make thread
t = Thread(target=continuous_read, args=(read_pins,))

# Start thread
t.start()

# Continue to use gpio to set other pins
gpio.set_bits(bits=(4, 7, 15))
gpio.set_bits(bits=(5, 8, 11))
gpio.unset_bits(bits=(4, 8, 15))
gpio.int_to_bits(bits=(12, 13, 14), val=7)

# Continue working...

# Stop thread
flag.set()
t.join()